maven
    注意powermock-api-mockito 2.0以上给项目重新起了个名字。

    1.         <dependency>
    2.             <groupId>org.powermock</groupId>
    3.             <artifactId>powermock-module-junit4</artifactId>
    4.             <version>2.0.9</version>
    5.         </dependency>
    6.         <dependency>
    7.             <groupId>org.powermock</groupId>
    8.             <artifactId>powermock-api-mockito2</artifactId>
    9.             <version>2.0.9</version>
    10.         </dependency>
    1. @RunWith(PowerMockRunner.class)
    2. @PrepareForTest({RedisKeyUtil.class})
    3. PowerMockito.mockStatic(System.class);
    4. PowerMockito.when(System.getenv("123")).thenReturn("123");